Filling with Argon gas instead of air will improve the insulating capacity of the double glazed unit. This is reflected by a lower U value than would result from the use of air. The magnitude of the benefit varies with the size of the gap between the glasses in the IGU. The use of Argon in a 12mm gap will result in an improvement of approximately 6%. Viridian only supply Argon gas as a standard across our complete double glazed range.